1. Field of the Invention
The present invention relates, in general, to a method for recycling aluminum dross, an oxide formed on the surface of the molten aluminum metal, to produce aluminum hydroxide (Al(OH).sub.3) powder, useful as a material for various aluminum compounds, and castable refractories.
2. Description of Prior Arts
Because aluminum is readily apt to be oxidized, aluminum dross is always produced whether at a large or small amount when aluminum is molten. When aluminum is founded into a base metal after being melted, aluminum dross is removed. When pouring molten aluminum metal into a mold, aluminum dross still remains, in part, in a furnace or a crucible. Even during the casting of molten aluminum metal, aluminum dross is generated at molten metal runners.
Typically, aluminum-melting factories melt aluminum dross by heating and reclaim aluminum metal out of the dross, so as to reduce the amount of aluminum dross to be discarded. Generally, this waste dross is treated by burial in earth. Usually, the waste dross finally produced comprises a predominant amount of aluminum oxide, 10.about.30% of aluminum metal, around 10% of salts and a mixture of impurities which originally exist in aluminum scraps, such as Mg, Si, Fe and the like.
In the case of treating aluminum dross in a conventional manner, it costs a great deal. For example, a burial site must be secured or a significant amount of money must be paid to waste disposal agents.
In order to prepare aluminum hydroxide, bauxite is conventionally used according to the Bayer process. For example, bauxite is dissolved at a high temperature under a high pressure in a sodium hydroxide (NaOH) solution to lixiviate aluminum oxide out of the ore into the solution, followed by hydrolyzing the solution to prepare aluminum hydroxide.
In this conventional method, a high temperature and a high pressure are required upon the decomposition of the ore, which is usually accomplished in an autoclave. In addition, it is certain that using aluminum dross in preparing aluminum hydroxide is more economically favorable than using bauxite.